Electronic piano with percussive effects employing zener operation



United States Patent [7 21 Inventor Michael R. Harris Cincinnati, Ohio [21] Appl. No. 763,654 I [22] Filed Sept. 30, 1968 [45] Patented Dec. 1, 1970 [7 3] Assignee D. H. Baldwin Company Cincinnati, Ohio a corporation of Ohio [54] ELECTRONIC PIANO WITH PERCUSSIVE EFFECTS EMPLOYING ZENER OPERATION 21 Claims, 3 Drawing Figs.

[52]- U.S.Cl 84/l.26, 84/l.l3 -[51] lnt.Cl. Gl0hl/02 [50] Field ofSearch 84/l.01,

[56] References Cited UNITED STATES PATENTS 2,897,361 7/1959 Schreiber 84/ 1.26X 3,383,453 5/1968 Sharp 84/126 3,440,324 4/1969 Schrecongostetal........ 3,465,088 9/1969 Kohls ABSTRACT: A control voltage terminal is connected in series with a key switch and further in series with two diodes, similarly poled, and with the base-emitter circuit of a transistor poled like the diodes. Across the first diode is conjnected a capacitor, across which may be applied voltages from tic. supplies, to control mode of operation of the system. To the base of the transistor via a high resistance may be applied Either of two do. voltages, to effect two control modes, these voltages including one negative value sufficiently great that the base-emitter circuit of the transistor can have Zener operation and another which does not permit Zener operation. A timing capacitor is connected from the emitter of the transistor to ground as an emitter load, and gate control voltage is derived therefrom for a tone controlling gate. A diode is connected across the timing capacitor, having its cathode connected to the emitter of the transistor, to provide a shunt path across the emitter load when the base-emitter junction operates in the Zener mode.

' PATEN-TED ntcl I976 SOLO 0 OFF YRS INVENTOR T4 M\CHAELR.HARR\S 7/144... .713 4, BY

M, 64: 9' ALI-14.1.4

ATTORNEYS ELECTRONIC PIANO WITH PERCUSSIVE EFFECTS EMPLOYING ZENER OPERATION BACKGROUND OF THE INVENTION A system for generating tone envelopes having any of a wide variety of characteristics in response to simple adjustments is of value in the art pertaining to electronic organs. Organs conventionally require a percussive tone, i.e., a tone which has a sharp rise which endures while a key is actuated, but which decays slowly on release of the key. In such systems availability of both long and short sustain is desired. However, it is also desirable to provide simulation of piano tones, which have a struck quality, i.e., which rise to a peak on key actuation and decay immediately thereafter in a sustain, which is cut short when the key is released. Pianos have pedal operated damper controls. These dampers are normally in contact with the strings when a key is not actuated and serve to provide a short sustain when in contact. Actuation of a pedal raises the dampers and permits a long sustain despite key release which however can be cut short any time by releasing the pedal.

My application Ser. No. 610,423, filed Jan. I9, 1967, entitled ELECTRONIC PIANO provides circuitry for simulating a piano tone electronically. In accordance with that application the peak amplitude of the produced tone is a function of the velocity of movement of the key. The present application dispenses with this feature of my prior application, with consequent simplification of circuitry.

SUMMARY OF THE INVENTION A tone envelope control system, which provides long and short sustain, or damped or undamped piano tone simulation, in response to selective switch operation. The circuit requires three diodes and one transistor, to develop gating control voltage having the required shapes, there being three selective switches which apply requisite combinations of control voltages to the diodes and to the base of the transistor. The transistor operates both in its normal switching mode and as a base-emitter Zener.

The system operates in the piano mode, selectively with damped or undamped operation, and in the percussive mode, to provide either long or short sustain.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic circuit diagram of a system according to the invention;

FIG. 2 is a schematic circuit diagram of an adjunct to the system of FIG. 1, arranged to provide coupling between manuals of an organ; and

FIG. 3 is a schematic circuit diagram of an adjunct to the system of FIG. 1, arranged to provide strike tone effects.

DESCRIPTION OF THE PREFERRED EMBODIMENT Assume that switch 10 is at contact 11, that switch 12 is at contact 13, and that switch l4.is at contact 15. This implies, assuming key switch K is open, V2 is 25.v., V3 is 20.v. and V4 is l5.v.; and thus l0.v. exists across C]. Current flows from ground through D3, the emitter-base circuit of transistor T (which conducts in Zener mode), resistence R1 to V3. the base of T being at the Zener potential below ground (about -l'.v.). The voltage of the emitter of T is applied to the gate control terminal 20, of gate 21, thus turning the gate off. Signal input to the gate is derived from source 22 in the form of square waves 22, and when the gate is conductive, signal output is developed across load resistance R2. The wave shape oi the latter depends on the character of the gate 21. A suitabte we is disclosed in my copending application Ser. No. 610,423, filed Jan. 19, 1967, and entitled ELECTRONIC Pl- ANO.

If now the key K is closed, Vl 0.v. is applied directly to plate 23 of C1. The remaining plate 23' of C1 is positive with respect to plate 23 by lO.v., and C1 cannot modify its potential instantaneously. Therefore, the plate 23 immediately on closure of switch K, assumes a voltage of +l0.v. with respect to ground, and this voltage commences forthwith to decay towards about 1 5.v. at V4, with a time constant of l5.ms. At the same time, current flows through diode D2 and into the base of T, which turns on (in conventional mode), charging C2 through resistance R4, with a time constant of .5 ms., to meet the decaying exponential at the cathode of D1, i.e., at plate 23'. When V,,, the gate control voltage (essentially the same as the voltage at the emitter of T), reaches +6.v. the base-emitter diode of T becomes back-biased, due to the relative decay times of the voltages applied to base and emitter, respectively, and its base thereafter continues negative, to be caught just below 0.v. by the circuit through D1 and D2 from ground and flowing through R1.

C2 now commences to decay through R5 into gate 21, with a time constant of 500 ms. A crucial point is that the voltage at the base of T decays more rapidly than the voltage at the emitter decays, so that T remains nonconductive through out the decay of voltage across C2.

When the key is released the cathode of D1 immediately falls below l5.v. back-biasing D2, which allows the baseemitter Zener diode of T to break down, and provide an additional discharge path for C2, through the Zener and R1. C2 is thus rapidly discharged, simulating piano damper action.

To lift the damper, switch 14 is moved to contact 15 which prevents breakdown of the Zener diode of T, when the key is released, because now when D2 is back-biased, the potential of the transistor base remains at 0. v. due to the ground connection through R1.

To operate the system in the percussive mode, switch 10 is moved to contact 9, at +8.v., switch 12 to contact 24 at l 5.v. and switch 14 to contact 15 at 20.v. This provides a short sustain, as follows.

Since plates 23 and 23 of C1 are both at l5.v. there is no initial charge thereon. On closing K, the cathode of D2 moves directly to keying potential, equal to +8.v. minus the small voltage drops in D1 and D2. T becomes conductive and remains so as long as K is depressed, maintaining gate 21 conductive. When key K is released, C2 discharges through R5 and R1 in parallel. The presence of 20.v. at switch 14 causes the base-emitter Zener of T to breakdown, causing a short sustain.

If, on the other hand, switch 14 is at contact 15, and is thus at 0.v., the Zener discharge path will not be available, and the entire discharge will be constrained to flow through R5 only, thus providing a long sustain.

In an actual organ, a keying circuit pursuant to FIG. 1 is provided for each key of a manual, only one such key K being illustrated in FIG. 1, but leads 27 being connected to further keys.

In FIG. 2 is illustrated how coupling from one manual to another may be accomplished. Here leads 27 to pertain to a solo header, and leads 27a to an accompaniment header. The solo keys are denoted K and the accompaniment keys are denoted K Each pair of keys of the same nomenclature proceeds via a diode, as D3 and D4 to a common point B; thereby, actuation of either key K or key K, will call forth the output of signal source 22. The point B in FIG. 2 is the keying point B of FIG. 1. Suppose it is desired to trigger the circuit from the solo manual but not the accompaniment manual in the percussion mode. Then points 27 will be at +8.v. and points 27a will be disconnected (at off position of switch 10a). Suppose D3 and D4 were not present; then when K and K, were closed at the same time, lead 27a would be connected to +8.v. If other accompaniment keys were depressed, circuits associated with them would be triggered. The presence of M prevents this from happening. Now, if it were desired to trigger the circuit from the accompaniment manual, but not the solo manual, D3 would prevent point 27 assuming the same potential as 27a (if K and K, were again closed concurrently).

Certain percussive voices require transient tones, called strike tones, i.e., tones which subsist on actuation of a key and a discharge device capable of being rendered conductive in response to discharge current from said capacitor, and connected to one plate of said capacitor;

a key operative when open to isolate the other plate of said capacitor from said source of control voltage and to connect said other plate of said capacitor to said source of v control voltage when closed; and

said discharge device being arranged and adapted to discharge only when said one plate of said capacitor is above a predetermined voltage, and said control voltage being such that said one plate of said capacitor exceeds the predetermined voltage only when said key is closed.

7 3. In a system for rendering a transistor conductive in response to a key switch closure:

a point of reference potential; I

a capacitor in cascade with said key switch;

a transistor having its base in cascade with said capacitor;

means for maintaining'a voltage across said capacitor and for maintaining the potentials of said plates of said capacitor substantially different from said reference potential, whereby opening and closing said key switch modifies the potential at said base; and I a diode connected in shunt to said capacitor.

4. The combination accordingto claim 3 wherein is provided: 7

a source of bias voltage selected to maintain said transistor normally nonconductive and a resistence connected directly between said source and said base: and

a further diode connected in series between said capacitor and said base and poled to isolate said capacitor from said source of bias voltage, said voltage across said capacitor being poled to pass current through said further diode to said base.

5. The combination according to claim 3, whereinis provided;

a second capacitor;

a second diode connected in parallel with said second capacitor and poled to retain the charge of said second capacitor identically with that of said first capacitor; and

means for modifying said voltage across said second capaciwt to zero and said voltage across said first capacitor to a value and polarity selected to render said transistor conductive in response to current flow through said diodes.

6. In a system for controlling the conductivity of an NPN transistor having a grounded emitter load:

a source of negative bias voltage;

a resistance connected between said source and the base of said transistor;

a capacitor; h v

a diode having its cathode connected to said base and its anode connected to one plate of said capacitor;

means applying to the plates of said capacitor two negative voltages, of which voltage applied to said one plate is the less negative; and l g means for at will connecting and disconnecting the other plate of said capacitor from ground.

7. The combination according to claim 6, wherein said load includes a second capacitor and wherein bias voltage is suffrciently great that said second capacitor when charged to a predetermined voltage can discharge from emitter to base of said transistor in the Zener mode.

8. A keying circuit for an electronic organ comprising: a transistor having a base, an emitter and a collector; a capacitive load connected between said emitter and reference point; i I a key;

means responsive to actuation of said key for transiently rendering the collector-emitter circuitof said transistor conductive to charge said capacitor to a predetermined.

level, and thereafter rendering said collector-emitter circuit of said transmitter nonconductive; and,

means responsive to the charging current only of said capacitor for generating a gating voltage.

9. A keying circuit foran electronic organ comprising;

an emitter load for said transistor, said emitter load includ-' ing a capacitor connected between said emitter and a reference point.

10. The combination according to claim 9, wherein is further provided a diode connected between said emitter and a reference point, said diode being poled to be nonconductive emitter current and to provide a path for Zener conduction through the emitter to base circuit of said transistor.

11. The combination according to claim 10, wherein is provided a further capacitor in series with said base:

means for normally maintaining the electrodes of said further capacitor at a voltage difference; and

a key responsive means for modifying the value of the voltage with respect to the ground of' one of said electrodes only of said further capacitor while inhibiting modification of said voltage difference.

12. In a keying circuit for an electronic organ:

a transistor having a base, an emitter and a collector;

means normally maintaining the collector-emitter path of said transistor nonconductive; i

a source of control voltage;

a capacitor;

a key switch connecting said source of control voltage to one terminal of said capacitor;

means connecting the other side of said capacitor to said base; and

means selectively applying to said capacitor terminals voltages different from each other and from said control voltage, and the same as each other but different from said control voltage.

13. A keying circuit for an electronic organ comprising: I

a transistor having a base, an emitter and a collector;

a capacitive-resistive load connected between said emitter and a reference point, said capacitive-resistive load including a capacitor and a resistor in series and resistance in shunt to said capacitor: I

a key; and

' means responsive to actuation of said key for applying to said base a transient voltage having a peak value such as to render said transistor conductive and a decay curve selected to render said transistor nonconductive sometime during the charging of said capacitor via said resistor.

14. The combination'according to claim 13, wherein is provided a diode shunting said capacitive load and having its cathode'connected to said emitter, and means biasing said transistor to operate in the Zener mode during discharge of said capacitor through said resistance in shunt to said capacitor.

15. A keying circuit for an electronic organ comprising:

a load circuit; r

an electronic switch connected to said load circuit;

a said electronic switch including a control electrode responsive to control voltage to render said electronic switch selectively conductive and nonconductive;

a capacitor in series with said control electode;

a key switch;

a diode inshunt to said capacitor;

means tending to maintain at least one fixed predetermined voltage across said capacitor to which said capacitor returns following a perturbation of the voltage across said capacitor; 1

means responsive to closure of said key switch for selectively applying to one plate of said capacitor only one of two diverse voltages, one of said diverse voltages and said voltage difference being such that said predetermined a discharge device capable of being rendered conductive in response to discharge current from said capacitor, and connected to one plate of said capacitor;

a key operative when open to isolate the other plate of said capacitor from said source of control voltage and to connect said other plate of said capacitor to said source of v control voltage when closed; and

said discharge device being arranged and adapted to discharge only when said one plate of said capacitor is above a predetermined voltage, and said control voltage being such that said one plate of said capacitor exceeds the predetermined voltage only when said key is closed.

3. In a system for rendering a transistor conductive in response to a key switch closure:

a point of reference potential;

a capacitor in cascade with said key switch;

a transistor having its base in cascade with said capacitor;

means for maintaining a voltage across said capacitor and for maintaining the potentials of said plates of said capacitor substantially different from said reference potential, whereby opening and closing said key switch modifies the potential at said base; and

a diode connected in shunt to said capacitor.

4. The combination according to claim 3 wherein is provided:

a source of bias voltage selected to maintain said transistor normally nonconductive anda resistence connected directly between said source and said base: and

a further diode connected in series between said capacitor and said base and poled to isolate said capacitor from said source of bias voltage, said voltage across said capacitor being poled to pass current through said further diode to said base. a

5. The combination according to claim 3, wherein is provided;

a second capacitor;

a second diode connected in parallel with said second capacitor and poled to retain the charge of said second capacitor identically with that of said first capacitor; and

means for modifying said voltage across said second capacitor to zero and said voltage across said first capacitor to a value and polarity selected to render said transistor conductive in response to current flow through said diodes.

6. In a system for controlling the conductivity of an NPN transistor having a grounded emitter load:

a source of negative bias voltage;

a resistance connected between said source and the base of said transistor;

a capacitor;

a diode having its cathode connected to said base and its anode connected to one plate of said capacitor;

means applying to the plates of said capacitor two negative voltages, of which voltage applied to said one plate is the less negative; and

means for at will connecting and disconnecting the other plate of said capacitor from ground.

7. The combination according to claim 6, wherein said load includes a second capacitor and wherein bias voltage is sufficiently great that said second capacitor when charged to a predetermined voltage can discharge from emitter to base of said transistor in the Zener mode.

8. A keying circuit for an electronic organ comprising:

a transistor having a base, an emitter and a collector;

a capacitive load connected between said emitter and reference point;

a key;

means responsive to actuation of said key for transiently rendering the collector-emitter circuit of said transistor conductive to charge said capacitor to a predetermined level, and thereafter rendering said collector-emitter circuit of said transmitter nonconductive; and

means responsive to the charging current only of said capacitor for generating a gating voltage.

9. A keying circuit for an electronic organ comprising;

a transistor having a base, an emitter and a collector;

means applying bias to said transistor for Zener conduction from said emitter through said base;

a key;

means responsive to actuation of said key for overcoming said bias only transiently and rendering the collectoremitter circuit of said transistor transiently conductive; and

an emitter load for said transistor, said emitter load including a capacitor connected between said emitter and a reference point.

10. The combination according to claim 9, wherein is further provided a diode connected between said emitter and a reference point, said diode being poled to be nonconductive emitter current and to provide a path for Zener conduction through the emitter to base circuit of said transistor.

11. The combination according to claim 10, wherein is provided a further capacitor in series with said base:

means for normally maintaining the electrodes of said further capacitor at a voltage difference; and

a key responsive means for modifying the value of the voltage with respect to the ground of one of said electrodes only of said further capacitor while inhibiting modification of said voltage difference.

12. ln a keying circuit for an electronic organ:

a transistor having a base, an emitter and a collector;

means normally maintaining the collector-emitter path of said transistor nonconductive;

a source of control voltage;

a capacitor;

a key switch connecting said source of control voltage to one terminal of said capacitor;

means connecting the other side of said capacitor to said base; and

means selectively applying to said capacitor terminals voltages different from each other and from said control voltage, and the same as each other but different from said control voltage.

13. A keying circuit for an electronic organ comprising:

a transistor having a base, an emitter and a collector;

a capacitive-resistive load connected between said emitter and a reference point, said capacitive-resistive load including a capacitor and a resistor in series and resistance in shunt to said capacitor:

a key; and

means responsive to actuation of said key for applying to said base a transient voltage having a peak value such as to render said transistor conductive and a decay curve selected to render said transistor nonconductive sometime during the charging of said capacitor via said resistor.

14. The combination according to claim 13, wherein is provided a diode shunting said capacitive load and having its cathode connected to said emitter, and means biasing said transistor to operate in the Zener mode during discharge of said capacitor through said resistance in shunt to said capacitor.

15. A keying circuit for an electronic organ comprising:

a load circuit;

an electronic switch connected to said load circuit;

a said electronic switch including a control electrode responsive to control voltage to render said electronic switch selectively conductive and nonconductive;

a capacitor in series with said control electode;

a key switch;

a diode in shunt to said capacitor;

means tending to maintain at least one fixed predetermined voltage across said capacitor to which said capacitor returns following a perturbation of the voltage across said capacitor; 7

means responsive to closure of said key switch for selectively applying to one plate of said capacitor only one of two diverse voltages, one of said diverse voltages and said voltage difference being such that said predetermined '7 voltage shifts while said diode remains nonconductive, and the other of said predeterm ned voltages being such and the polarity of said diode being such that said diode conducts current while said predetermined voltage remains fixed; and whereby selection of said diverse voltages determines whether said keying circuit will operate in' a percussive or a piano mode. 16. In a keying circuit for an electronic organ: a key switch; circuit means responsive to closure of said key switch and maintenance of said closure for generating a-rapidly rising tone signal followed by a slowly decaying tone signal; and

means responsive to opening of said switch following said closure and during said slowly decaying tone for accelerating the decay of said tone, to provide a piano response of said electronic organ.

17. The combination according to claim 16 wherein is further provided means modifying said circuit means to effect, in response to said closure of said key switch, a level tone during said closure of said switch and a slow sustain of said tone on subsequentopening of said switch, to provide an organ response of said electronic organ.

18. The combination according to claim 17 wherein is further provided means for at will providing speed up of said slow sustain.

19. In a keying circuit for an electronic organ;

a solo key switch;

an accompaniment key switch;

a control point;

a source of selective solo control voltages and a source of accompaniment control voltages selectively percussive tone characteristics for solo tones and accompaniment tones, respectively;

a tone signal source;

a first diode connected between said solo key switch and said control point;

a second diode connected between said accompaniment key switch and said control point; and

said diodes being poled identically with eachpther and with respect to said control point and so poled as to pass said control voltages to said control point 20. The combination according to claim 19, wherein said control voltages are respectively zero and a positive value of at least several volts for each of said solo and accompaniment tone signals.

21. A strike tone system for an electronic organ comprising:

a tone signal source responsive to an applied voltage for providing a tone signal source;

a plurality of gating control devices;

means responsive to actuation of adjacent keys of said electronic organ for selectively rendering said gating control devices operative to provide a separate control voltage and means responsive to any one or more of said control voltages for generating a strike tone common to all said control voltages. 

